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In page Flag Desecration Amendment:

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The theories underlying these First Amendment principles include: a robust national discourse about political and social ideas; individual self-realization; the search for truth; and speech as a "safety valve". These concepts are expounded in both the majority and dissenting opinions of the cases described below. There Justice William Joseph Brennan, Jr. noted that the "principal function of free speech under our system of government is to invite dispute; it may indeed best serve its high purpose when it induces condition of unrest, creates dissatisfaction with conditions as they are, or even stirs people to anger".[1]